Heretofore, it has been attempted to achieve an improvement in combustion of an engine by controlling a flow, such as a tumble flow or a swirl flow, of gas in a combustion chamber. For example, there has been known a technique of causing an air-fuel mixture to be gathered within a piston cavity or to be transferred to the vicinity of an electrode of a spark plug, in a spark-ignited direct-fuel injection engine (see, for example, Patent Document 1).